Open Data supplied by Natural Environment Research Council (NERC)

Bissett-Berman 9060 Salinity Temperature and Depth

The B-B 9060 STD measured salinity, temperature and depth and whose analogue output was in graphical form. The plots created were of salinity and temperature versus depth which had to be manually digitised.

Instrumentation

The instrument used was a Bissett Berman STD system and the data were logged on a Hewlett Packard 9820. Instrument lowering and raising speeds between 0.5 m/s and 1 m/s. An acoustic pinger was placed above the STD to give an accurate depth measurement, this could then be used to check the STD pressure calibration. An NIO bottle with reversing thermometers was placed above the pinger, within 2m of the STD system. A bottle sample was taken at the bottom of the cast providing the temperature and salinity are uniform at that point. If large temperature or salinity gradients were present then the bottle sample was triggered at a suitable site on the upcast. A surface salinity sample was also taken at the start of the dip.

Calibration

The STD was not calibrated in the laboratory. The manufacturer's calibration was used and water samples taken to check the calibration and apply corrections where necessary.

Temperature

The manufacturer's calibration was used to convert the raw data to physical units using the equation below:

Temperature (°C) = (10 6 /Pt - 2238.68)/55.84 where Pt is the temperature period in microseconds

These values were then plotted against the water bottle (i.e. reversing thermometer) temperatures and a regression line fitted to the data such that:

Temperature(WB) = m x Temperature(STD) + c

Then the regression coefficients (m and c) were applied to correct the STD temperature data - these are given in the table below.

Salinity

The manufacturer's calibration was used to convert the raw data to physical units using the equation below:

These values were then plotted against the STD salinity and a regression line fitted to the data such that:

Salinity(WB) = m x Salinity(STD) + c + (m1 x Pressure + c1)/1000

Then the regression coefficients were applied to correct the STD salinity data. The data showed a salinity - pressure dependency, this was corrected by plotting delta-S (i.e. calibrated salinity - calculated salinity) against pressure to determine the slope (m1) and intercept (c1). These were then incorporated into the equation as shown above. The regression coefficients are given in the table below.

Pressure

The depths from the acoustic pinger were noted where the bottle samples were taken and then used to check the calibration of the pressure sensor - unless calibration values were available from the reversing thermometers. The equation below was used to convert the pressure period to physical units.

Pressure = (10 6 /Pd - 9712)/0.26267 where Pd is the pressure period in microseconds

A regression fit was carried out using the calibration values and the slope and intercept determined. The pressure values could then be corrected using:

Pressure (CORR) = m x Pressure(STD) + c

The fit of the STD data to the water bottle calibration data for each leg of the cruise is given in the table below:

Cruise 11/78 leg A

Variable

Slope (m)

Intercept (c)

Standard Deviation

Temperature (°C)

1.0000

0.0688

0.006

Salinity (ppt)

1.0744

-2.4278

0.015

Pressure (dbar)

1.0299

-34.9755

1.451

Delta-S

-0.0049

0.5594

13.260

Cruise 11/78 leg B

Variable

Slope (m)

Intercept (c)

Standard Deviation

Temperature (°C)

1.0003

-0.0385

0.009

Salinity (ppt)

0.9257

2.9132

0.002

Pressure (dbar)

1.0282

15.6677

1.535

Delta-S

0.0041

-9.7990

5.590

Cruise 11/78 leg C

Variable

Slope (m)

Intercept (c)

Standard Deviation

Temperature (°C)

1.0009

-0.0428

0.006

Salinity (ppt)

0.8955

3.9406

0.011

Pressure (dbar)

1.0103

9.3642

6.381

Delta-S

-0.0113

20.5965

5.365

Cruise 11/78 leg D

Variable

Slope (m)

Intercept (c)

Standard Deviation

Temperature (°C)

1.0005

-0.0392

0.006

Salinity (ppt)

1.0075

-0.0059

0.032

Pressure (dbar)

0.9544

12.2749

Delta-S

0.0236

-12.7160

27.047

Data Processing

Obvious wild points were edited out of the calibration file and the calibration programs run to obtain values for the slopes and intercepts for temperature, pressure and salinity. These were then applied to the uncalibrated data and sigma-t was calculated. The data values were then sieved to ensure a minimum separation between pressure values of 1 dbar. The data were then visually inspected and major spikes flagged.